Constructing valve positioners for hazardous areas

ABSTRACT

A controller for a valve assembly that is configured to meet requirements for use in hazardous areas. These configurations may regulate flow of instrument air to a pneumatic actuator to operate a valve. The controller may comprise enclosures, including a first enclosure and a second enclosure, each having a peripheral wall forming an interior space, and circuitry comprising a barrier circuit disposed in the interior space of one of the enclosures that power limits digital signals that exits that enclosure. In one example, the peripheral wall of enclosures are configured to allow instrument air into the interior space of the first enclosure but to prevent instrument air from the interior space of the second enclosure.

BACKGROUND

Flow controls are important in many industries. Whether found on processlines, distribution networks, or any system that carries flowingmaterial, devices like valve assemblies are vital to regulate materialflow within set parameters. Sometimes, these devices must operate inhazardous areas. Valve assemblies, for example, may mount onto processlines that carry flammable or combustible materials, like natural gas.In such cases, it is important that these devices meet certain designspecifications to prevent ignition of the material.

SUMMARY

The subject matter disclosed herein relates to improvements that meetthese design specifications. Of particular interest are embodiments ofcontrol hardware that meets both explosion-proof and intrinsically-safedesign standards. This control hardware, or “controller” or “valvepositioner,” may integrate onto the flow device to control mechanicalmechanisms to regulate this flow. For valve assemblies, these mechanismsmay include an actuator, likely pneumatic, that manages movement of aclosure member relative to a seat via a stem. During operation, thecontroller may receive and processes a control signal from a processcontrol system (also “distributed control system” or “DCS system”). Thecontrol signal may define operating parameters for the valve assembly.These operating parameters may set an appropriate flow of materialthrough the valve assembly and into the process line. The controller cantranslate the operating parameters, often in combination with the outputfrom the position sensor, to regulate instrument gas into the actuator.The instrument gas may pressurize (or de-pressurize) the actuator in away that moves the valve stem and, in turn, locates the closure memberin position relative to the seat to coincide with the operatingparameters.

DRAWINGS

Reference is now made briefly to the accompanying drawings, in which:

FIG. 1 depicts a schematic diagram of an exemplary embodiment of acontroller for use to control a valve assembly;

FIG. 2 depicts a schematic diagram of an example of the controller ofFIG. 1;

FIG. 3 depicts a schematic diagram of exemplary topology for a barriercircuit for use in the controller of FIG. 1;

FIG. 4 depicts a schematic diagram of an example of the controller ofFIG. 1; and

FIG. 5 depicts a perspective view of structure for an example of thecontroller and valve assembly of FIG. 1.

Where applicable, like reference characters designate identical orcorresponding components and units throughout the several views, whichare not to scale unless otherwise indicated. The embodiments disclosedherein may include elements that appear in one or more of the severalviews or in combinations of the several views. Moreover, methods areexemplary only and may be modified by, for example, reordering, adding,removing, and/or altering the individual stages.

DETAILED DESCRIPTION

The discussion that follows describes embodiments of a controller foruse with flow devices and fluid control. The controller is shown tooperate with a valve assembly, but the concepts may percolate to otherfluid regulating devices (e.g., pressure regulators), particularly thosethat are for use in hazardous areas. The embodiments have a modulardesign that separates functional elements into independent, operativemodules. Some of these modules may be configured to minimize operatingpower and temperatures to meet guidelines and requirements typical of“intrinsically-safe designs.” Other modules are built to satisfyexplosion-proof standards. When combined, the modules adapt thecontroller to meet both intrinsically-safe and explosion proof standardsand still have appropriate functionality so that the valve assembly canregulate fluids in hazardous areas. Other embodiments are within thescope of the subject matter herein.

FIG. 1 depicts a schematic diagram of an exemplary embodiment of acontroller 100 that meets requirements for use in hazardous areas. Thecontroller 100 is useful to operate a process device, identifiedgenerally by the numeral 102 and discussed herein as a “valve assembly.”In this regard, the valve assembly 102 may have an actuator 104,typically pneumatic, that couples with a valve 106 via a stem 108. Thevalve 106 may include one or more valve components (e.g., a closuremember 110 and a seat 112). The valve assembly 102 may integrate into aprocess line 114, often by coupling in-line with a conduit 116 thatcarries material 118. The valve assembly 102 may also couple with aprocess control system 120 that is configured with a main control loop122 that provides one or more signals (e.g., a loop control signal C anda power signal P). The system 120 may also include a pneumatics supply124 that provides instrument air 126. As also shown, the controller 100may have an architecture that disperses functionality acrossexplosion-proof devices 128 and intrinsically-safe devices 130. Thearchitecture may also include a safety barrier 132 disposed between thedevices 128, 130. In one implementation, the devices 128, 130 mayinclude a main control device 134 that manages functions of thecontroller 100. The main control device 134 couples with one or moreperipheral devices (e.g., a first device 136, a second device 138, and athird device 140).

Broadly, the controller 100 is configured to satisfy requirements forboth explosion-proof and intrinsic-safety on a “single” device. Theseconfigurations separate operative functions into self-contained devices.Each device has functionality that comports with its respective safetycharacterization (whether explosion-proof or intrinsically-safe). Thesefeatures may simplify design as compared to practices to date, oftenreducing burdens to appropriately arrange, size, and fit components toaddress both safety standards. The explosion-proof devices 128 may housepower “hungry” functionality (like data processing and diagnostics)because these devices do not limit incoming energy. Further, unlikeprior practices, the embodiments separate pneumatic functions from theexplosion-proof devices 128 to the intrinsically-safe devices 130. Thisfeature is beneficial because it eliminates “openings” in theexplosion-proof devices 128 that would allow for ingress of pressurized,instrument air, which tends to complicate packaging design decisions inorder to meet certifications for explosion protection.

The valve 106 is configured to regulate flow of material 118. Closuremember 110 may embody a plug, a ball, a butterfly valve, and/or likeimplement that can contact a seat to prevent flow. A sensing mechanismmay be useful to monitor the position of the closure member 110 relativeto the seat 112. This sensing mechanism can have a position sensor and amechanical linkage that couples the position sensor with the stem orother structure that moves in concert with the closure member. In someexamples, the actuator 104 includes a pneumatic actuator that convertsenergy (e.g., compressed instrument air 126) into mechanical motion tocause the closure member 110 to move between an opened position, apartially opened position, and a closed position.

The safety barrier 132 may be configured to comport with“intrinsically-safe circuit designs.” These configurations may embodycircuitry (or circuits) that are effective to power or “energy” limitsignals, preferably those signals that enter areas that are notexplosion-proof. In one implementation, the circuitry can ensure signalsfrom the main control device 134 are at low voltages and low currents.

The main control device 134 may be configured to act as the central“brains” of the controller 100. These configurations may havefunctionality to control or instruct operation of the devices 136, 138,140. Suitable functions may process signals, including the controlsignal C, and other inputs to the main control device 134. These inputsmay correspond with signals that originate from the devices 136, 138,140, which may also be at the voltage and current levels to meetintrinsically-safe environments. In this regard, the main control device134 may be configured for the control signal C to assume any industrialautomation protocols. Examples of these protocols include HART, 4-20milliamp, FOUNDATION Fieldbus, or Profibus. In use, the main controlloop 122 may provide the main control device 134 with proper control(via the loop control signal C) and power (via the power signal P). Inone implementation, power available from the main control loop power 122may be approximately 40 milliwatts.

The first peripheral device 136 may be configured to operate theactuator 104. This “pneumatic” configuration may include hardware andsoftware to provide a pneumatic signal to the actuator 104. Thepneumatic signal may be regulated instrument air 126 that effectivelyraises or lowers pressure at the actuator 104 to manage movement of theclosure member 110 relative to the seat 112. Often, the pneumatic signalcorresponds with a control signal from the main control device 136. Thiscontrol signal may itself correspond with the loop control signal C,which the control system 122 uses to set flow of the material 120through the valve assembly 102.

The second peripheral device 138 may be configured to allow an end userto interact with the main control device 136. This “interactive”configuration includes features to exchange information with the enduser. Example features may incorporate display technology to visualizedata and information. The features may also include various inputdevices (e.g., buttons, keyboards, touchscreens, etc.) that can allowthe end user to input data, read data, or make selections that influenceoperation or modes on the controller 100.

The third peripheral device 140 may be configured expand functionalityof the controller 100. This “options” configuration may provide certainfunctions that are not essential to the controller 100 to operate thevalve assembly 102. Exemplary options may include sensor technology todetect leaks, vibrations, or position of the closure member 110. Otheroptions may offer wireless communication technology. End users mayselect from among several available options to install onto thecontroller 100.

FIG. 2 depicts a schematic diagram of an example of the controller 100.In this example, the devices 134, 136, 138, 140 leverage a housingstructure that can meet explosion-proof standards. This housingstructure uses multiple enclosures 142, each having a peripheral wall146 that creates an interior space 148. A communication interface 150may be configured to permit exchange of signals, preferably digitalsignals (e.g., S₁, S₂, S₃) and power signals (P₁, P₂, P₃). Theseconfigurations may include connectors 152 that may couple with orincorporate into the peripheral wall 148, where necessary. Wiring 154may extend between connectors 152 to couple the main control device 136with the devices 138, 140, 142. The pneumatic device 138 may alsoinclude a pneumatic fitting 156 to delivers instrument air 126 to thisdevice. As also shown, the devices 134, 136, 138, 140 may includecircuitry to enable functions on these devices. On the main controldevice 134, the circuitry may embody barrier circuitry 158 that operatesas the safety barrier 140 to power limit the outgoing digital signalsS₁, S₂, as desired. The circuitry may also include a control part 160and a functional part 162 across all of the devices 134, 136, 138, 140.Bus structure 162 may be used to exchange digital signals to theconnectors 152. Examples of the bus structure 164 may utilize standardor proprietary communication busses including I²C, UART, SPI, UNI/O,1-Wire, or one or more like serial computer busses known at the time ofthe present writing or developed hereinafter.

The housing structure allows devices 134, 136, 138, 140 to couple withone another to form the controller 100 as a functional, modular “unit.”Often, the enclosure 142 of the main control device 134 may operate as a“base” to receive the other, peripheral devices 136, 138, 140. Fastenerslike bolts may be useful to ensure safe, secure attachment. Whenassembled, the pneumatic device 136 may receive instrument air 126directly through pneumatic fittings 156. But the peripheral wall 146prevents ingress of instrument air 126 into the interior space 148 ofthe main control device 134. This feature maintains the interior space148 as safe for use with higher-power functions to occur or to househigh-power devices.

Enclosures 142 may be configured to meet relevant operative standardsfor the respective devices 134, 136, 138, 140. For devices 136, 138,“first” enclosures may satisfy only “intrinsically-safe” designs, wherethe peripheral wall 146 may comprise plastic or metals, like sinteredmetals or formed metal sheets, often at the discretion of the installenvironment. Some designs may favor materials that are flame-retardant.It is recognized, as well, that the intrinsically-safe “first”enclosures 142 may not require any external structure at all. On thedevices 134, 140, “second” enclosures may meet “explosion-proof”standards, where the peripheral wall 146 may comprise cast, machined, orformed metals with appropriate vents and like pressure-dissipatingfeatures built therein. Suitable materials may comport with U.L. 1203standards, where applicable.

The peripheral wall 146 may adapt to provide ready access to theinterior space 148. These adaptations may use multi-piece structuresthat include separable “sections” of the peripheral wall 146. Thesections can connect together with fasteners (e.g., bolts, screws, etc.)or “quick-release” snaps, clips, or fittings. But care should be takento ensure appropriate and secure fits that comport with explosion proofstandards at least on the explosion-proof devices 128.

The communication interface 150 may facilitate communication across themodular architecture. The devices 134, 136, 138, 140 may incorporateappropriate computing components (e.g., processor, memory, sensors,etc.) to process and generate the digital signals S₁, S₂, S₃. Thisfeature allows the devices 136, 138, 140 to easily swap out of thecontroller 100 in lieu of, for example, a replacement device withcomparable functionality. Connectors 152 may include pin-and-socket orlike elements to enable this “quick release” capability. In lieu ofwiring 154, preference may also be given to outfit the controller 100with a circuitized substrate (e.g., a printed circuit board) withconnections or connectors 152 and appropriate trace topology. Thisconfiguration could allow devices 136, 138, 140 to “plug” into thecircuitized substrate to transmit signals S₁, S₂, S3, P₁, P₂, P₃ amongthe devices.

The pneumatic fitting 156 can permit instrument air 126 to penetrate theenclosure 142 of the device 136. Quick-release fittings that engage tubeor tubing are likely candidates for this design. The pneumatic fitting156 resides separate or independent of the explosion-proof enclosures128. This location prevents ingress of pressurized air into theexplosion-proof housing of the main control device 134 (and from theoptions devices 140, as well). As noted above, this feature isbeneficial because it reduces cost and complexity of the design of theenclosures 142 and allows the devices 134, 140 to operate at powerlevels that are greater than the devices 136, 138, thus allowing forenhanced or improved functionality.

FIG. 3 depicts a schematic digram of topology 166 for an example of thebarrier circuitry 158. Components in the topology 166 can be arranged tocreate two zones, e.g., a hazardous zone Z_(H) and a safe zone Z_(S).The topology 166 terminates at the connectors 152, typically a two-wireinterface that “exits” to the hazardous zone Z_(H) which for purposes ofthis example is typically found outside of the explosion-proof housing150 of the main control device 136. Inside of the safe zone Z_(s), thetopology 166 may include discrete devices (e.g., a fuse 168 and aresistor 170). A diode device 172 couples the discrete devices 168, 170to a ground 174. Examples of the diode device 172 may include one ormore zener diodes, but other discrete devices may work as well. Inoperation, fault voltage across the barrier circuit 166 will causecurrent to flow across the diode device 172 to the ground 174. Thegrounded current causes the fuse 170 to open, thus limiting currentavailable to the intrinsically-safe devices 138, 140 via connectors 152.

FIG. 4 depicts a schematic diagram of additional details for circuitrythat facilitates functions on the controller 100. The control part 160may include computing components like a processor 176 and memory 178with data 180 stored thereon. Data 180 may comprise executableinstructions, like software, firmware, and like computer programs.Processor 176 may also communicate with driver circuitry 182, whichoperates to interface with other components, for example, bus structure164 (e.g., bus, wires, connectors, etc.). As also shown, the controlpart 160 may include a power supply 184. This device may provide powerthat energizes the computing components to meet requirements for thecontroller 100 to communicate via the automation protocol (e.g., HART,FOUNDATION Fieldbus, etc.). Collectively, the computing components mayintegrate together as a microcontroller or like solid state device. Onthe main control device 134, the parts 160, 162 may form a main controlboard that is operative to manage functions, including to provideinstructions for operation of the functional part 162 on other, remotedevices 136, 138, 140 of the controller 100. The functional part 162 onthe pneumatic control device 138 may be configured to regulate flow ofinstrument air to the actuator 104. This configuration may include apneumatic control, shown here as a signal converter 186 that coupleswith an amplifier 188. A sensor 190 may be useful as well. Examples ofthe sensor 190 may measure pressure, temperature, and like parameters.On the interactive device 140, the functional part 158 may be configuredto facilitate user interaction with the controller 100. It may providecertain peripheral controls (e.g., display 192 and pushbutton input194), as desired. The options device 142 may include one or more devices196 for different options.

In operation, the controller 100 may cause the actuator 104 to move theclosure member 110 to an instructed position. The main control board onthe main control device 134 can process the control signal C to generatean input signal I_(s), typically electrical current. The pneumaticcontrol device 136 can use (or process) the input signal I_(s) tostimulate the signal converter 186, such as a current-to-pneumatic (I/P)converter, to generate a proportional pneumatic pressure output P_(s)(also, “signal pressure P_(s)” or “pilot pressure P_(s)”). Flowmodifying structure on the amplifier 188 may integrate components (e.g.,diaphragms, valves, etc.) into a single or unitary package with, forexample, an input for the instrument air 132, an input for the signalpressure P_(s), and an output port. Collectively, these components maybe analogous to pneumatic relays and like devices that, when combinedtogether, can generate, a pneumatic actuator signal P_(a) to operate theactuator 104. In one implementation, the structure may leverage one ormore diaphragms that move in response to the signal pressure P_(s). Thisdiaphragm may operate an internal valve (or valves) to modulate theinstrument air 126 to generate the pneumatic actuator signal P_(a) thatexits the output port. The pneumatic actuator signal P_(a) may haveparameters that are proportional to the signal pressure P_(s) atbalanced conditions. Sizing of internal components and flow coefficients(C_(V)) for the flow modifying structure may influence parameters forthe pneumatic actuator signal P_(a).

The display 192 may be configured to provide visual representation orindication. These configurations may embody an LCD display, typicallyalpha-numeric, or like device. This display may present values for thecontrol signal, valve position, or actuator pressure. For touchcreenimplementations, the display 184 may further provide appropriateactuatable inputs, like icons, touch-sensitive buttons, and the like.

The pushbutton input 194 may operate as the primary local user interfaceto allow the end user (e.g., a technician) to change settings, readouts,and like operative features. Notably, practice to date may require theuser interface to meet “explosion” proof standards, which may requirestiffer more robust dials and actuatable member. The input 194 may offerbetter, easier actuation because it meets only “intrinsic-safetyrequirements. This feature may be important for regular maintenance,configuration, and setup, for example, to allow the end user to exitfrom valve operating mode and step through a menu structure to manuallyperform functions such as calibration, configuration, and monitoring.

Optional devices 196 may be configured to expand functionality on thecontroller 100. These configurations may include sensors that canmonitor parameters of flow, whether of material 118 or instrument air132. In some implementations, the sensor may be particularly configuredto collect other operating date from the valve assembly 102. Thisoperating data may be used in diagnostics that can help schedulepreventive maintenance and like tasks. In this regard, the devices 196may also include wireless technology, like antenna orreceivers/transmitters, so as to property convey the data from thedevice.

FIG. 5 depicts a perspective view of an example of the controller 100installed onto exemplary structure 200 for the valve assembly 102. Thisstructure may be useful to regulate process fluids in industrial processlines typical of industries that focus on chemical production, refiningproduction, and resource extraction. As shown, the structure 200 caninclude a fluid coupling 202 that forms a flow path with open ends(e.g., a first open end 204 and a second open end 206). Valve componentslike the closure member 110 and seat 112 may reside inside of the bodyand hidden in the present view. The structure may also include apneumatic, diaphragm actuator 208 with a bulbous housing 210, typicallywith two pieces that clamp about the edges to entrap a diaphragm (notshown) round the periphery. As noted herein, the actuator often turnspressurized instrument air 126 (FIG. 3) into mechanical motion thatcauses the closure member 110 to move relative to the seat 112 between,for example, an open position, a partially-open position, and a closedposition. Although not depicted in FIG. 5, a sensing mechanism may beused to monitor the position of the closure member 110. This sensingmechanism can have a position sensor and a mechanical linkage thatcouples the position sensor with the valve stem 108 or other structurethat moves in concert with the closure member 110.

In view of the foregoing, the embodiments offer proper safety measuresfor use on valve assemblies that operate in hazardous areas. But theconcepts here also simplify the design by spreading functionality acrossdifferently-configured devices. In this way, the resulting controllermay be built to be both intrinsically-safe and explosion-proof, butavoid the cost and time intensive design efforts that are oftennecessary to meet these standards at the time of this writing.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. An element or functionrecited in the singular and proceeded with the word “a” or “an” shouldbe understood as not excluding plural said elements or functions, unlesssuch exclusion is explicitly recited. References to “one embodiment” ofthe claimed invention should not be interpreted as excluding theexistence of additional embodiments that also incorporate the recitedfeatures. Furthermore, the claims are but some examples that define thepatentable scope of the invention. This scope may include andcontemplate other examples that occur to those skilled in the art. Suchother examples are intended to be within the scope of the claims if theyhave structural elements that do not differ from the literal language ofthe claims, or if they include equivalent structural elements withinsubstantial differences from the literal language of the claims.

Examples appear below that include certain elements or clauses one ormore of which may be combined with other elements and clauses describeembodiments contemplated within the scope and spirit of this disclosure.

What is claimed is:
 1. A valve assembly, comprising: a valve; apneumatic actuator coupled to the valve; and a controller pneumaticallycoupled with the pneumatic actuator, the controller comprising a firstenclosure and a second enclosure, each having a peripheral wall formingan interior space, and circuitry comprising a barrier circuit disposedin the interior space of the second enclosure that power limits digitalsignals that exit the second enclosure, wherein the peripheral wall ofthe first enclosure and the second enclosure are configured to allowinstrument air into the interior space of the first enclosure but toprevent instrument air from the interior space of the second enclosure.2. The valve assembly of claim 1, wherein the controller comprises amain control board disposed in the second enclosure and coupled withbarrier circuit to generate the digital signals in response to a loopcontrol signal from outside of the second enclosure.
 3. The valveassembly of claim 1, wherein the controller comprises a pneumatic relaydisposed in the first enclosure.
 4. The valve assembly of claim 1,wherein the controller comprises a current-to-pressure converterdisposed in the first enclosure.
 5. The valve assembly of claim 1,wherein the controller comprises a processor and memory in the firstenclosure that generates a digital signal that exits the firstenclosure.
 6. The valve assembly of claim 1, wherein the first enclosurecomprises a pair of devices, each detachable from the second enclosureindependent of the other.
 7. The valve assembly of claim 6, wherein oneof the devices generates a pneumatic signal to the actuator.
 8. Thevalve assembly of claim 6, wherein one of the devices provides apushbutton interface.
 9. The valve assembly of claim 1, wherein thesecond enclosure comprises a pair of devices that are detachably securedto each other via connectors and wiring and disposed in separate piecesof the second enclosure.
 10. The valve assembly of claim 1, wherein thesecond enclosure is explosion-proof.
 11. A valve assembly, comprising: apneumatic actuator; a first enclosure pneumatically coupled with thepneumatic actuator, the first enclosure having a pneumatic fitting toallow ingress of instrument air; a second enclosure electrically coupledwith the first enclosure; and barrier circuitry interposed between thefirst enclosure and the second enclosure, the barrier circuitry powerlimiting digital signals before the digital signals enter the firstenclosure, wherein the first enclosure and the second enclosure have aperipheral wall that prevents flow of instrument air from the firstenclosure to the second enclosure.
 12. The valve assembly of claim 11,wherein the barrier circuitry is disposed in the second enclosure. 13.The valve assembly of claim 11, further comprising: a third enclosureelectrically coupled with the second enclosure, the third enclosurecomprising a display responsive to digital signals from the secondenclosure.
 14. The valve assembly of claim 11, further comprising: afourth enclosure electrically coupled with the second enclosure, whereinthe fourth enclosure is explosion-proof
 15. The valve assembly of claim11, wherein circuitry in the first enclosure operates at power levelsthat are less than circuitry in the second enclosure.
 16. The valveassembly of claim 11, further comprising: a signal converter; and anamplifier coupled with the signal converter, wherein both the signalconverter and the amplifier are disposed in the first enclosure.
 17. Amethod, comprising: separating circuitry on a valve assembly between afirst enclosure and a second enclosure that are rated for a first powerlevel and a second power level that is greater than the first powerlevel, respectively; and operating an actuator using the circuitry by,at the first enclosure, generating a digital signal in response to aloop control signal; and at the second enclosure, converting instrumentair into a pneumatic signal that moves the actuator in response to thedigital signal at the first enclosure.
 18. The method of claim 17,further comprising: power limiting the digital signal to the first levelat a barrier circuit in the second enclosure.
 19. The method of claim17, further comprising: receiving the instrument air at only the firstenclosure.
 20. The method of claim 17, wherein the first enclosure andthe second enclosure form an interior space that is enclosed andindependent of one another.